On/off switch...

The Pi doesn't like being suddenly disconnected from the power, this is a full Linux distro and therefore likes to be shutdown properly before being powered off.

If you dial a 6 on the phone, wait until it ring through, it will shut down the Pi. Now the power can be shut off by switching off the power.

On the back one connection if obviously the receiver, the other is used for the USB plug to the LiPo battery. Nice and neat!